• extension of input pre-processing Methods of pre-processing of the input snippets, performed by the other modules of the Carrot2 system, such as stemming or stop-words removal also have a strong influence on the final results. We feel that for instance extension of stop-lists would result in a considerable improvement of result clusters quality as descriptions of clusters created by our algorithm often consist of single terms only. This fact makes them unclear in case when these terms are ones which contain no information and should in fact be put on the stop-list.

• overlapping clusters Unfortunately, in results given by AHC one document may appear only in one group (not counting its parent groups in hierarchy). Yet in the real world single documents may correspond to several different topics and should be contained in an appropriate number

- 86 of clusters. However, during our work on this thesis we haven't found any publications

mentioning attempts to create version of the AHC algorithm with such capabilities.

• improvement of usefulness of created clusters We feel that main problem with the quality of AHC results is that it quite often creates clusters made up from documents which share just one or two single words, which usually don't tell us anything about their real topic. So rejecting some of the created clusters and moving documents contained in them to the "Other Topics" group may have in fact an overall good influence on the results.

• speed of implementation Unfortunately, our implementation of the AHC algorithm is certainly too slow for its practical application. Main reason of this fact is the cubic complexity of used version of the clustering algorithm itself.

Scatter/Gather: a cluster-based approach to browsing large document collections, Proceedings of the 15th International ACM SIGIR Conference on Research and Development of Information Retrieval (SIGIR'92): 318-329, 1992.

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